Manganese-Catalyzed Epoxidations of Alkenes in Bicarbonate Solutions

Abstract

This paper describes a method, discovered and refined by parallel screening, for the epoxidation of alkenes. It uses hydrogen peroxide as the terminal oxidant, is promoted by catalytic amounts (1.0-0.1 mol %) of manganese(2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Peroxymonocarbonate, HCO(4)(-), forms in the reaction, but without manganese, minimal epoxidation activity is observed in the solvents used for this research, that is, DMF and (t)BuOH. More than 30 d-block and f-block transition metal salts were screened for epoxidation activity under similar conditions, but the best catalyst found was MnSO(4). EPR studies show that Mn(2+) is initially consumed in the catalytic reaction but is regenerated toward the end of the process when presumably the hydrogen peroxide is spent. A variety of aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using 10 equiv of hydrogen peroxide, but monoalkyl-alkenes were not. To improve the substrate scope, and to increase the efficiency of hydrogen peroxide consumption, 68 diverse compounds were screened to find additives that would enhance the rate of the epoxidation reaction relative to a competing disproportionation of hydrogen peroxide. Successful additives were 6 mol % sodium acetate in the (t)BuOH system and 4 mol % salicylic acid in the DMF system. These additives enhanced the rate of the desired epoxidation reaction by 2-3 times. Reactions performed in the presence of these additives require less hydrogen peroxide and shorter reaction times, and they enhance the yields obtained from less reactive alkene substrates. Possible mechanisms for the reaction are discussed.

Chemiluminescence Energy Transfer Reaction for the On-Line Preparation of Peroxymonocarbonate and Eu(II)−Dipicolinate Complex

“…A mixing coil that is either too long or too short could not produce the most HCO 4 -ions. To examine the HCO 4 -ions of on-line preparation, we used 98% 13 C-enriched NaHCO 3 to examine bicarbonate-peroxide in ethanol/water solvents by 13 C NMR at 25°C. Hydrogen peroxide concentration of 2.0 mol/L was employed, and [H 13 CO 3 -] ) 0.05 mol/L for all studies.…”

“…Ethanol/water (1.76:1, v/v) solutions of hydrogen peroxide with bicarbonate catalyst were mixed 10 min prior to the experiment to ensure the preequilibration of peroxymonocarbonate formation for the whole experiment. 13 C NMR spectral measurements were carried out on an Avance DPX 400 MHz NMR instrument (Bruker, Germany). H 2 O 2 (10%) was replaced by D 2 O.…”

Room Temperature Epoxidation of Alkenes With Hydrogen Peroxide Catalyzed by Heteropolyoxometalate

“…Therefore, the development of efficient routes for catalytic epoxidation under mild conditions using inexpensive terminal oxidants remains as an important challenge in synthetic chemistry. Recently, catalytic epoxidation reaction in presence of hydrogen peroxide (H2O2) as terminal oxidant has attracted much attention [6][7][8][9][10][11][12][13] because: (i) It generates only water as a side product. (ii) It contains the largest amount of active oxygen species among the known oxidants, and (iii)…”

Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in-situ in Ionic Liquids

“…There is a bulging need for the elaboration of catalytic systems that consume only cheap, ecologically friendly and readily available oxidants, such as hydrogen peroxide [3,4]. In this context our group reported very recently about the ability of certain anions of ionic liquids, such as tetrafluoroborate and perrhenate, to activate hydrogen peroxide through only hydrogen bonding interactions [5,6].…”